Thermal Decomposition of Aluminum Chloride Hexahydrate

The decomposition rate of aluminum chloride hexahydrate (AlCl3·6H2O) was measured as weight loss at ambient pressure and elevated temperatures up to 270 °C. Such incomplete thermal decomposition produces a porous and reactive basic aluminum chloride [Al2O3·2HCl·2H2O or Al2(OH)4Cl2·H2O] which dissolves in water to give poly(aluminum chloride) used as an efficient flocculation agent. A slowly rising temperature method and very small sample masses, which minimize heat and mass transfer intrusions, were employed to determine intrinsic reaction rates. A fractional order kinetic equation of Arrhenius type was proposed for the decomposition and tested also against the results amassed by experiment in a constant temperature mode. This correlation allows the estimation of the reaction rate as a function of temperature and the extent of decomposition. It can be readily employed in modeling and simulation of the decomposition process. The contents of aluminum and chlorine in the decomposed solids were also explored in the course of the decomposition process. Pore volume (porosity), pore-size distribution, and BET surface area data were also collected on decomposed chloride particles.